Hydraulic control system

Abstract

A hydraulic control system of a vehicle power train having a belt-type continuously variable transmission, and a hydraulic lock-up clutch, includes: a line pressure control valve; first and second control valves; first, second and third electromagnetic valves; and a fail-safe valve. The fail-safe valve is switched to a fail position in which a line pressure is supplied to one of a drive pulley and a driven pulley when a rapid deceleration state is likely to occur in the belt-type continuously variable transmission, the fail-safe valve is switched to a normal position in which a hydraulic pressure output from the first control valve is supplied to the one of the drive pulley and the driven pulley during times other than the above, and the fail-safe valve is switched by a combination of a hydraulic pressure controlled by the second electromagnetic valve and a hydraulic pressure controlled by the third electromagnetic valve.

Description

INCORPORATION BY REFERENCE[0001]The disclosure of Japanese Patent Application No. 2008-109390 filed on Apr. 18, 2008 including the specification, drawings and abstract is incorporated herein by reference in its entirety.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The invention relates to a hydraulic control system of a vehicle power train.[0004]2. Description of the Related Art[0005]Some of known power trains mounted on vehicles include a belt-type continuously variable transmission, a hydraulic lock-up clutch, and the like. The belt-type continuously variable transmission clamps a belt by hydraulic pressure to transmit power, and changes the belt winding diameters to vary speed ratios. The hydraulic lock-up clutch is provided in a fluid power transmission device that is arranged in a power transmission path between a power source and the belt-type continuously variable transmission.[0006]A hydraulic control system of such a vehicle power train includes a large n...

AI Technical Summary

Benefits of technology

[0011]The invention provides a hydraulic control system that is able to avoid occurrence of a rapid deceleration state in a belt-type continuously variable transmission without providing an additional electromagnetic valve.

[0013]With the above hydraulic control system, when a rapid deceleration state is likely to occur in the belt-type continuously variable transmission, the fail-safe valve is switched to the fail position to supply the line pressure to the one of the drive pulley and the driven pulley of the belt-type continuously variable transmission. Thus, it is possible to avoid occurrence of a rapid deceleration state. That is, it is possible to suppress a variation in the speed ratio to the deceleration side by introducing the line pressure to the one of the drive pulley and the driven pulley. Then, it is possible to prevent a belt slip, an overrevolution, an axle lock, or the like, that may occur in accordance with rapid deceleration. In addition, because the existing electromagnetic valves (the second electromagnetic valve and the third electromagnetic valve) are used for switching the fail-safe valve, it is possible to avoid an increase in cost and an increase in size of the system.

[0016]With the above hydraulic control system, both the second electromagnetic valve and the third electromagnetic valve are used for switching the fail-safe valve. Thus, in comparison with the case in which the fail-safe valve is switched by a single solenoid, it is possible to narrow the range used in the event of a failure, the range being set for each of the hydraulic pressure controlled by the second electromagnetic valve and the hydraulic pressure controlled by the third electromagnetic valve. Hence, it is possible to suppress an increase in source pressure of each of the second electromagnetic valve and the third electromagnetic valve in accordance with setting of the range used in the event of a failure, and, as a result, it is possible to suppress the flow rate consumed by each of the second electromagnetic valve and the third electromagnetic valve. In addition, it is possible to suppress an increase in control gain of each of the second electromagnetic valve and the third electromagnetic valve in accordance with setting of the range used in the event of a failure, and, therefore, it is possible to suppress deterioration of controllability of each of the hydraulic pressure controlled by the second electromagnetic valve and the hydraulic pressure controlled by the third electromagnetic valve.

[0017]In addition, in regard to each of the hydraulic pressure controlled by the second electromagnetic valve and the hydraulic pressure controlled by the third electromagnetic valve, a range used to switch the fail-safe valve to the fail position may overlap a range used for control during normal times. By so doing, it is possible to prevent an increase in source pressure of each of the second electromagnetic valve and the third electromagnetic valve, and, therefore, it is possible to prevent an increase in control gain of each of the second electromagnetic valve and the third electromagnetic valve.

[0020]By so doing, the fail-safe valve is returned to a state before being switched to the fail position, so the line pressure is not introduced to the one of the drive pulley and the driven pulley. Thus, a variation in the speed ratio to the acceleration side is inhibited, thus allowing the speed ratio to vary to the deceleration side again. Thus, when the vehicle stops, the vehicle may start running again in a state where the speed ratio is set in a full deceleration state or a state close to the full deceleration state. As a result, it is possible to avoid a situation that driving force is insufficient.

[0026]According to the aspect of the invention, it is possible to suppress a variation in the speed ratio to the deceleration side by introducing the line pressure to the one of the drive pulley and the driven pulley of the belt-type continuously variable transmission. Then, it is possible to prevent a belt slip, an overrevolution, an axle lock, or the like, that may occur in accordance with a rapid deceleration. In addition, because the existing electromagnetic valves (the second electromagnetic valve and the third electromagnetic valve) are used for switching the fail-safe valve, it is possible to avoid an increase in cost and an increase in size of the system.

Problems solved by technology

Incidentally, in the hydraulic control system, control valves or electromagnetic valves that control the control valves may fail because of a mechanical factor, such as a valve stick, or may fail because of an electrical factor, such as a disconnection or a short-circuit in the electromagnetic valves.

However, the hydraulic control system of the existing belt-type continuously variable transmission supplies a shift hydraulic pressure to the drive pulley only from the shift hydraulic pressure control valve.

Thus, if the shift hydraulic pressure control valve or the electromagnetic valve that controls the shift hydraulic pressure control valve fails, a shift hydraulic pressure controlling a speed ratio may steeply decreases, causing the belt-type continuously variable transmission to be placed in a rapid deceleration state.

This problematically leads to an increase in cost and an increase in size of the system.

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